The Google team responds with the following

Your app does not contain a full-size app banner or is it not visible in the launcher. We are targeting 1080P, which we consider xhdpi. Apps should include the banner in the xhdpi (320 dpi) drawables folder with a size of (320px × 180px). Please refer to our Home Screen Banner and UI Patterns documentation.

The title should help users identify apps in the launcher. Please refer to our Visual Design and User Interaction documentation for more information.

For example, your banner does not fill the entire banner space.

The app is developed with ionic 4, how could I solve this inconvenience?

While I have never done any Android TV development, those resources are defined in the config.xml file that Cordova reads and merges into the android manifest. You might need to manually build your in Android Studio and edit the files directly.